An eccentric screw pump essentially comprises a screw-shaped rotor mounted rotatably in a stator, which rotor rotates with its longitudinal axis eccentrically around the stator axis. The side of the stator facing the rotor comprises an at least double-lead helix having a double pitch and corresponding to the rotor shape. A plurality of chambers of equal size arises between the rotor and the stator, in which chambers the delivered material, on account of the different pitches of the rotor and the stator, is moved in its axial direction through the stator. The rotor is usually made from a low-abrasion material such as steel for example, and the stator is made from an elastic material, such as rubber for example.
The elastomer body is often provided in practice with a casing, the stator being vulcanised for example into the casing. On account of its material, the stator is subject to a comparatively high degree of wear, for which reason a replacement of the stator or the stator casing is required at regular intervals. Solutions have repeatedly been sought in the past to keep the maintenance work required for a replacement to a minimum.
An eccentric screw pump with a stator casing is disclosed for example in DE 102 41 753, said stator casing comprising, for the purpose of simplifying the assembly and dismantling of the elastomer body, a stator casing comprising a plurality of segments connected to one another and extending in the longitudinal direction. The longitudinal edges of the segments are constituted in such a way that adjacent segments engage into one another in order to create a form-fit connection capable of being subjected to tensile loads. Furthermore, the segments are constituted in such a way that their sides facing the elastomer body essentially form flat surfaces. A closed casing in a polygonal shape thus arises through the connection of a plurality of segments. This polygonal shape engages in a corresponding polygonal shape of the outer side of the elastomer body, so that a form fit results for the transmission of the torque and a rotational motion of the elastomer body in the stator casing is prevented.
It would however be desirable for a stator with a stator casing and an elastomer body to be made available, with which not only a rotational motion of the elastomer body is impeded. Since, during the pump operation, in particular as a result of the delivery motion of the rotor, radial and axial forces also occur which act on the elastomer body, the fixing of the elastomer body should be further improved. A special embodiment is known for example from WO2011/155312, wherein the elastomer body is provided at both its ends with a collar, as a result of which effective sealing of the pump is intended to be achieved. The collar is disposed in a recess between the stator casing and a connection body (connection flange, pump housing). The stator casing and the elastomer body are clamped between the connection flange and the pump body by means of threaded rods, the distance arising between the stator casing and the connection body being smaller than the thickness of the collar, as a result of which the collar is squashed and a sealed connection thus arises between the stator and the connection body. Although the elastomer body is also fixed axially in this way, the radially acting forces in the region of the collar are however taken up solely by the constituted friction-locked connection.
The problem underlying invention, therefore, is to provide a stator casing of the type mentioned at the outset, which enables improved fixing of the elastomer body.